Process of making and using thermographic reproduction paper



June 22, 1965 s. c. HUETT ETAL 3,191,030

PROCESS OF MAKING AND USING THERMOGRAPHIC nnrnonucwzon PAPER Filed Nov. 2, 1962 r, V V V I 6 n H 3 INVENTORSI RGE C. HUETT TWELL L. 8 GS CORNELIUS B. L YER JOSEPH W, WARTON ATT 'YS United States Patent Office 3,191,030 Patented June 22, 1965 3,191,030 PRGCESS OF MAKING AND USING THERMO- GRAIHIC REPIEGDUCTION PAPER George C. Huett, Hartwell L. Briggs, Cornelius E. Lawyer, and Joseph W. Wartou, Chicago, Ill., assignors to Eugene Dietzgen Co., Chicago, Ill., a corporation of Delaware Filed Nov. 2, 1962, Ser. No. 235,015

7 Claims. (Cl. 25065) The subject invention relates to the production of thermographic paper. More particularly, the present invention is directed to improved copying materials which are capable of producing a facsimile copy by means of radiant energy.

In the past several years, various types of copy paper have been developed which produce a facsimile copy when exposed to radiant energy such as infrared light beneath graphic subject matter set forth on an original. A typical thermographic process is described in the patent to Miller, US. 2,740,896. As is disclosed in this patent, carbon inks and certain other marking means absorb radiant energy from infrared bulbs creating heat. This energy is transferred to a sensitized sheet of copy paper in contact with the original causing the formation of duplicate characters.

A wide variety of materials have been used as color producing bodies in coating the copy paper. In heat developable diazotype reproduction systems, for example, the copy paper is coated with a diazo compound, a coupler, and a compound which produces an alkaline reaction when heated. In other systems such materials as nickel acetate, silver nitrate, sodium behenate, ferric stearate, etc., have been used as components of the color producing coating.

In diazotype photoprinting processes the diazo component is sensitive to light and the coupler component is capable of reacting with the diazo component to form a dye. In making a print, the treated base such as paper or a plastic film is exposed to light under a translucent original or master. In those areas of the base which are reached by the light the diazo compound is at least partially destroyed. In those areas that are beneath opaque lines or designs, on the other hand, the diazo compound is not affected by the light. The print is developed by reacting the retained diazo compound with a coupler to form a highly colored azo dyestuff in precise duplication of the original. In an alternative method, heat is transferred from the graphic characters of the original directly to the treated base. The heat causes a reaction to take place between the coupler and the diazo compound which forms a precise duplication of the original characters. Thereafter, the remaining diazo compound is destroyed by exposing the treated copy sheet to ultraviolet light or the like. Diazotype reproduction processes are classified as either moist processes or dry processes. In a moist process the base is coated with a diazo compound which is exposed to light under a pattern. Thereafter, color development is brought about by contacting the latent diazo image with a solution of a coupling compound and aqueous alkali. In the dry process the light sensitive layer contains both the diazo compound and a coupler together with acids and various other stabilizing substances. After the treated base has been exposed to light the print is formed by the use of hot aqueous ammonia fumes.

Each of the above systems has serious disadvantages. The principal objection to the dry process is that it requires the use of ammonia fumes. Because of the pungent and corrosive nature of the fumes it is necessary to provide special venting devices before the process can be used to any great extent. Although the moist process does not require the use of ammonia fumes it has the disadvantage that the developing solution must be mixed frequently because it is susceptible to oxidation. Furthermore, the evaporation of water from the developer causes crystallization to occur and often leaves a sticky mass on the developing machine.

Many attempts have been made to provide practical two-component thermographic diazotype reproduction materials which can be used in place of systems requiring developing solutions and/or alkaline vapors. Until very recently, these efforts for the most part were unsuccessful. Difficulties arose because of the dual need to prevent premature reaction between the diazo compound and the coupling component and to cause a rapid reaction between the components at the desired time. In the first heat developable systems, satisfactory shelf life was only accomplished at the expense of print quality. Stabilizing methods such as placing the coupler within a gelatin coating and dusting powdered coupler on the diazo coated paper prevented precoupling but also resulted in the development of faint and weak reproductions.

More recently, a heat developable diazotype system has been developed which is feasible from a commercial standpoint. In this system a layer containing an intimate mixture of a diazo compound, an azo coupling component, and an alkali generating compound is formed on a suitable base. A solution of the various materials is brushed or otherwise applied to the base. Following the removal of volatiles from the liquid coat, the paper, cloth, plastic, etc., is ready for photoprinting.

Even though the most recent developable processes provide commercially acceptable results, there is still room for improvement both as to the shelf life of the coated materials, and as to the color density and sharpness of the resultant reproduction.

It is an object of the present invention to provide an improvement in the known thermographic reproduction processes.

Another object of the invention is to provide a new type of heat reactive copy papers which can be used to make reproductions from originals printed on one or both sides.

Another object of the invention is to provide diazotype thermographic reproduction paper which can produce sharp and well defined copies which can be used as read out copies or intermediates.

Still another object is to provide heat developable diazotype photoprinting materials which have an excellent shelf life.

Other objects of the invention will become apparent to those skilled in the art from the following detailed description of the invention.

In general, the present invention comprises the discovery that improved thermographic reproduction material is obtained by coating a suitable base with a solution containing a diazo complex, a suitable organic acid, and a stabilizing agent. If it is desired a binder resin can be added to the formula. Under conditions of the process, the diazo complex undergoes a molecular rearrangement to form an azoic dye. The rearrangement reaction takes place under acid conditions. After the base has been coated with the sensitizing solution the copy paper is placed in contact with an original which can be printed on one or both sides. The resultant sandwich is subjected to radiant energy such as visible light in the orange and red spectral zones, or invisible infrared radiation. If a reflex technique is used the radiant energy passes through the heat-sensitive copy material whereupon it is absorbed by the characters of the original producing heat which is transmitted to the reproduction material. If a direct trans mission technique is used, the radiant energy is focused on the original (printed only on one side), the characters of 3 which absorb the energy, convert it to heat, and cause the formation on the copy material of characters duplicating the characters of the original. The heat transferred to the copy material initiates an intramolecular rearrangement reaction on the treated sheet leading to the formation of a highly colored azoic dye.

In the subject process, a stable salt of a diazo compound and a sulfonic acid coupler is formed in such a way that when the coating containing the complex and the organic acid is heated, the complex need only undergo a molecular rearrangement to produce the dye. A minor amount of a stabilizing agent such as thiourea, biuret, triethanolamine, urea, etc., can be incorporated in the coating formulation in order to improve the shelf life of the treated paper. The diazo complex, organic acid, stabilizing agent, and binder resin (if such is desired) are dissolved in a suitable solvent and the resultant solution is applied to the base material. Thereafter, the volatile constituents of the solution are removed.

Examples of compounds which can be used as starting materials in the production of the stable diazo salt include the following:

p-Arnino-N,N-dimethylaniline p-Amino-N,N-dipropylaniline p-Amino-N,N-diethylaniline p-Amino-N-ethyl-N-propylaniline p-Amino-N-ethylaniline p-Amino-N-ethyl-N-fi-hydroxyethylaniline p-Amino-N-methyl-N-fi-hydroxyethylaniline p-Amino-N,N-di-5-hydroxyethyaniline p-Amino-m-ethoxy-N,N-diethylaniline p-Amino-N-ethyl-o-toluidine p-Amino-N-ethyl-m-toluidine p-Amino-N,N-diethyl-m-toluidine p-Amino-N-ethyl-N-hydroxyethy1-m-toluidine p-Amino-N-ethyl-N-benzylaniline p-Amino-N-ethyl-N-fi-hydroxyethyl-m-toluidine N-p-amino-phenylmorpholine N- (2, 5 -diethoxy-4-aminophenyl -morpholine p-Amino-diphenylamine 3-Aminocarbazole, and the like Stabilized salts of the following diazos (usually the zinc chloride salt) are the preferred compounds for forming the complex:

N-benzoyl-2,5-dibutoxy ethoxy p-diazo aniline N-acetyl-2,5-dibutoxy ethoxy p-diazo aniline V N-dialkyl-2,5-diethoxy butoxy p-diazo aniline N-diaryl-2,5-diethoxy butoxy p-diazo aniline p-Diazo aniline p-Diazo-2,5-dialkoxy (halo) aniline N-morpholino-Z,S-dialkoxy (halo) aniline N-substituted p-diazo anilines, etc.

The diazo salts preferably are reacted with the sodium salt of 2,3-dihydroxy naphthalene-6-sulfonic acid to form the complex.

The acids that are used to trigger the formation of the azo dye are organic acids having dissociation constants varying from that of citric acid to that of benzene sulfonic acid. Our preferred acids include the following:

Meta-benzene disulfonic acid Benzene sulfonic acid p-Toluene sulfonic acid Benzene trisulfonic acid Citric acid Sulfanilic acid The amount of acid that is used in the process can vary from about 0.5 g. to about 5 g. per 50 g. of solvent. The amount of acid that is used in the process can vary from about 0.1 gram to about 2.0 grams per gram of diazo complex, and preferably from about 0.2 gram to 1.0 gram per gram of diazo complex.

' Any one of a large number of organic solvents can be used in producing the subject copy paper. These solvents 4, can include alcohols such as ethanol, isopropanol, and butanol, and Cellosolves such as butyl Cellosolve, as Well as ketones and aliphatic and aromatic hydrocarbons, cyclohexane, benzene, and toluene.

If it is desired, stabilizing agents such as urea, biuret, thiourea, triethanolamine, triphenylphosphate, tributylphosphate, tricresylphosphate, symmetrical dimethyl urea, symmetrical diphenyl urea, allyl thiourea, dithiobiuret, and dimethylol urea can be used in the formulation. The amount of stabilizer can vary from about 0.1 gram to about 0.5 gram per 50 grams of solvent.

The invention is illustrated in the attached schematic drawing in which:

FIGURE 1 is an enlarged fragmentary cross-section of a sheet of reproduction paper embodying the invention and shown in print making relation to a cross-section of the original to be copied; and

FIGURE 2 is an enlarged fragmentary cross-section of a sheet of reproduction material which illustrates a modified process which may be practiced in carrying out the subject invention.

The reproduction or copy material 1 illustrated in the drawing is composed of a sensitive layer 2 on a base 3. The sensitive layer 2 consists of paper which has been treated with a solution containing an acid and a diazo complex.

FIG. 1 illustrates a reflex process which constitutes a preferred embodiment of the invention. In this process, the sheet of reproduction material 1 containing sensitized layer 2 on base 3 is superimposed on master or original 4 forming an exposure sandwich S. The master consists of a sheet or base layer 5 of paper or graphically markable sheet material containing a design, drawing, Written or typed character 6 to be copied. As is indicated in the figure, character 6 can be on both sides of the sheet in the reflex system. Radiations Re such as visible light in the orange and red spectral zones as well as invisible infrared radiation is produced by radiation source 7. The radiations Re pass through the copy material 1 and strike the face surface 8 of original 4. Radiation striking character 6 of master 4 are converted to heat which is conducted as indicated at H to the sensitive layer 2 of the reproduction material. An image 6" is produced which duplicates original character 6. Radiations that are not absorbed either are reflected as shown at 9 or are transmitted through the materials. Where the original is printed on both sides, the unabsorbed radiations are reflected by adjusting radiations Re. The radiations are focused on the surface of the copy paper in an elongated zone normal to the face of the sandwich, while the sandwich moves with respect to said zone in the direction of the arrow. If it is desired, the base 3 can be coated or synthesized on both sides. Under these circumstances, the print would appear both on the front and the back of the copy sheet.

In FIG. 2 an alternate method is described in which reproduction material 1 is beneath master or original 4. Once again, the master consists of a sheet or base layer 5 of paper or graphically markable sheet material containing a design, drawing, written or typed character 6 to be copied. The master is superimposed on the sheet of reproduction material 1 to form an exposure sandwich S. Radiations Re such as visible light in the orange and red spectral zones as well as invisible infrared radiation is produced by radiation source 7. The radiant energy source 7 preferably is arranged so as to scan the original and copy materials. Radiations Re are concentrated and focused on the face surface 8 of the original in an elongated zone normal to the face of the drawing, While the sandwich moves with respect to said zone in the direction of the arrow. As each portion of the sandwich passes through the focal zone, radiations are absorbed by the design area 6 and are converted to heat, which, as shown at H, is conducted through the base 5 of the original 4, to the sensitive layer 2 of the copy material. The heat causes a rearrangement of the complex to form into duplicate character 6".

The radiations which are not absorbed by character 6 are reflected as is illustrated at 9, or they may be transmitted through base of the original depending upon the materials used. These rays normally do not affect the reproduction if the original contains a design only on its face surface.

The following examples are illustrative of the subject invention.

Example 1 In this example reproduction paper was treated with a composition made up of the following ingredients:

Diazo complex (2,3-dihydroxy naphthalene-6- sulfonic acid complex salt of N-benzoyl-2,5- dibutoxy ethoxy p-diazo aniline) 3.0 Citric acid 3.0 Solvent (ethanol) 50.0 Stabilizing agent (thiourea) 0.1 Binder resin 1.0

The solution was applied to the paper with a solution-wet roller, although other suitable means could be used such as spraying, kiss coating, slot fountain, etc. After the excess was removed the paper was dried for about two minutes in a drying oven held at 60-80" C. and was superimposed on an original containing typed graphic characters. The sandwich was placed beneath an infrared bulb whereby the characters on the original were reproduced on the copy paper by a reflex system such as is illustrated in FIG. 1 of the drawing. An excellent reproduction of the original was obtained by this method. The temperature produced in the paper by the infrared bulb was about 350 F. The characters of the facsimile were black to violet in color.

Example 2 In this example, reproduction material having a visible light transmission characteristic of greater than 30% was treated with a composition made up of the following ingredients:

Diazo complex (2,3-dihydroxy naphthalene-6-sulfonic acid complex salt of N-benzoyl-2,5-dibutoxy ethoxy p-diazo aniline) 1.0 mBDSA 1 1.0 Solvent (ethyl Cellosolve) 50.0 Stabilizing agent (thiourea) 0.2 Binder resin 2.0

1 Metabenzene disulfonic acid.

In this test the solution was applied to the paper with a solution-wet roller. After the excess had been removed the paper was dried in an oven held at 70 C. The treated paper was placed in sandwich relationship with a superimposed original having typed graphic characters which were black in color. The sandwich was placed beneath an infrared bulb whereby radiation from the bulb was absorbed by the graphic characters on the original. Heat was transferred to the copy paper which caused the complex to rearrange whereby characters formed on the base duplicated the characters of the original. The reproduction had good contrast and was satisfactory in all respects. The characters of the copy print were black to violetbrown in color.

Example 3 In this example, cellulosic reproduction material was treated with a composition made up of the following ingredients:

G. Diazo complex (2,3-dihydroxy naphthalene-6-sulfonic acid complex salt of N-acetyLLS-dibutoxy ethoxy p-diazo aniline) Organic acid (p-toluene sulfonic acid) 0.5

Solvent (ethanol) 50.0 Stabilizing agent (biuret) 0.1 Binder resin 1.0

The solution was again applied to the paper with a solution-wet roller. After the excess was removed the paper was dried in an oven in the manner described in Example 1. The treated copy paper was superimposed on an original containing typed graphic characters. The resultant sandwich was placed beneath an infrared bulb whereby the characters on the original were reproduced on the copy paper by a reflex system which is described in connection with FIG. 1 of the drawing. Once again, an excellent reproduction of the original was obtained by this method. The characters of the reproduction were black to violet in color.

As has been indicated above, it is sometimes of ad-' vantage to use a binder resin to hold the applied coatings to the surface of the base. Such a resin can be watersoluble or water-emulsifiable polymers such as polyvinyl acetates, acrylic type polymers, phenol-formaldehyde resins, water-soluble alkyd resins, etc.

The subject reproduction paper and method have a number of advantages over reflex copy papers that are now in use. The use of diazo complexes in the manner described produces Well defined characters of a highly advantageous color. The paper has excellent stability with regard to aging. The produced copies also can be used either as read outs or as intermediates, and are useful as masters for offset printing. The copies that are made are permanent and contain a high degree of contrast between developed image print and background. The composition likewise is relatively low in cost.

Due to the presence of the acid the composition is believed to undergo two chemical reactions. The first reaction involves a breakdown of the cellulose of the paper into reducing type carbohydrates. These carbohydrates, after being dehydrated and cyclicizcd to furfural type derivatives, polymerize to form colored polymers. The second reaction involves the rearrangement of the diazo complex into an azo dye. The first reaction occurs to a lesser extent than the second reaction.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for graphically reproducing an original which comprises: placing an original having preferential radiation absorbing areas in contact with a layer of a visibly heat-sensitive composition supported on a cellulosic substrate, said composition containing a 2,3-dihydroxy naphthalene-6-sulfonic acid complex salt of a diazo compound, and an organic acid having a dissociation constant varying from that of citric acid to that of benzene sulfonic acid, and thereafter irradiating said original with heat producing radiations to eifect a molecular rearrangement of said diazo complex to form an azoic dye whereby said original is visibly reproduced.

2. A process as in claim 1 wherein the amount of organic acid varies from about 0.01 gram to about 5.0 grams per gram of the complex salt of the diazo compound.

3. A process as in claim 1 wherein the amount of organic acid varies from about 0.2 gram to about 2.0 grams per gram of the complex salt of the diazo compound.

a. A process as in claim 1 wherein said organic acid is selected from the group consisting of meta-benzene disulfonic acid, benzene sulfonic acid, p-toluene sulfonic acid, benzene trisulfonic acid, citric acid, and sulfanilic acid.

5. A process for producing a thermally developable copy sheet which comprises: applying a solvent solution of an organic acid and a 2,3-dihydroxy naphthalene-6 sulfonic acid complex salt of a diazo compound to a cellulosic base, said organic acid having a dissociation constant varying from that of citric acid to that of benzene sulfonic acid, the amount of organic acid being from about 0.1 gram to about 5.0 grams per gram of said complex salt of the diazo compound, and thereafter drying said treated base.

6. A process for producing a thermally developable copy sheet which comprises: applying a solvent solution of an organic acid and a 2,3-dihydroxy naphthalene-6- sulfonic acid complex salt of a diazo compound to a cellulosic base, said organic acid having a dissociation constant varying from that of citric acid to that of benzene sulfonic acid, the amount of organic acid being from about 0.2 gram to about 2.0 grams per gram of said complex salt of the diazo compound, and thereafter drying said treated base.

8 '7.A process as in claim 5 wherein said organic acid is selected from the group consisting of meta-benzene disulfonic acid, benzene sulfonic acid, p-toluene sulfonic acid, benzene trisulfonic acid, citric acid, and sulfanilic acid.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Kosar: Photographic Sci. and Eng, vol. 5, No. 4, July-August 1961, pp. 239-243.

WILLIAM D. MARTIN, Primary Examiner. MURRAY KATZ, Examiner. 

1. A PROCESS FOR GRAPHICALLY REPRODUCING AN ORIGINAL WHICH COMPRISES: PLACING AN ORIGINAL HAVING PREFERENTIAL RADIATION ABSORBING AREAS IN CONTACT WITH A LAYER OF A VISIBLY HEAT-SENSITIVE COMPOSITION SUPPORTED ON A CELLULOSIC SUBSTRATE, SAID COMPOSITION CONTAINING A 2,3-DIHYDROXY NAPHTHALENE-6-SULFONIC ACID COMPLEX SALT OF A DIAZO COMPOUND, AND AN ORGANIC ACID HAVING A DISSOCIATION CONSTANT VARYING FROM THAT OF CITRIC ACID TO THAT OF BENZENE SULFONIC ACID, AND THEREAFTER IRRADIATING SAID ORIGINAL WITH HEAT PRODUCING RADIATIONS TO EFFECT A MOLECULAR REARRANGEMENT OF SAID DIAZO COMPLEX TO FORM AN AZOIC DYE WHEREBY SAID ORIGINAL IS VISIBLY REPRODUCED. 